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Electrical Principles and Wiring Materials

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Electricity is a form of energy that can produce light, heat, ... lights dim, motors overheat. larger wires have less voltage drop for a given amount of current ... – PowerPoint PPT presentation

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Title: Electrical Principles and Wiring Materials


1
Electrical Principles and Wiring Materials
  • Unit 31

2
Principles of Electricity
  • Electricity is a form of energy that can produce
    light, heat, magnetism, chemical changes
  • Resistance tendency of a material to prevent
    electrical flow
  • Conductor if electricity flows easily
  • Insulator material that provides great resistance

3
Amps, Volts, Watts
  • Amperes measure of the rate of flow of
    electricity in a conductor
  • Volts measure of electrical pressure
  • Watts measure of the amount of energy or work
    that can be done
  • Ohms measure of electrical resistance to flow

4
Ohms Law
  • Ohm R
  • Volts E
  • Amps I
  • Ohms Law E IR
  • IE/R
  • RE/I

5
Electrical Safety
  • Shock and Fire
  • Never disconnect any safety device
  • Dont touch electrical items with wet hands or
    feet
  • Dont remove ground plug prong
  • Use GFI in wet areas
  • Discontinue use of extension cord that feels warm
  • Dont put extension cords under carpet

6
Electrical Safety
  • Install wiring according to NEC
  • Blown fuse or breaker, determine cause
  • Dont replace fuse with larger fuse
  • Dont leave heat producing appliances unattended
  • Heaters lamps away from combustibles
  • Dont remove back of TV (30,000v when off)
  • Electric motors lubricated, free of grease etc.

7
Electrical Safety
  • Keep appliances dry
  • Dont use damaged switches, outlets, fixtures,
    extension cords
  • Follow manufacturers instructions for
    installation and use of electrical equipment

8
Service Entrance
  • Power from from power company
  • Transformer drops volts from 25,000 volts to 240
    volts
  • Service drop wires etc from transformer to house
  • Entrance head weather-proof at house
  • Meter
  • Service Entrance Panel (SEP) box with fuses or
    breakers

9
Electric Meter
  • Kilowatthours how electricity is sold
  • Kilo 1000
  • Watthour use of 1 watt for one hour
  • 100 watt light bulb for 1 hour - 100 watthours
  • Kilowatthour 1000 watts for one hour

10
Branch Circuits
  • usually begin at SEP
  • branch out into a variety of places
  • only 1 motor or
  • series of outlets or
  • series of lights
  • use correct size wire and fuse or breaker

11
Types of Cable
  • Nonmetallic sheathed cable copper or alluminum
    wire covered with paper, rubber, or vinyl for
    insulation
  • Armored cable flexible metal sheath with
    individual wires inside. Wires are insulated
  • Conduit tubing with individually insulated wires

12
Wire Type and Size
  • copper
  • No 14 (14 gauge) 15 amp circuits
  • No 12 20 amps
  • No 10 30 amps
  • aluminum use one size larger
  • lower gauge number larger wire
  • No 8 and larger use bundles of wires
  • current travels on outer surface of wire, so a
    bundle of smaller wires can carry more

13
Voltage Drop
  • loss of voltage as it travels along a wire
  • lights dim, motors overheat
  • larger wires have less voltage drop for a given
    amount of current
  • longer wire greater problem
  • must increase wire size as distance increases

14
Wire Identification
  • Type of outer covering, individual wire covering,
    cable construction, number of wires
  • Wire type stamped on outer surface

15
Wire Types
  • Type T - dry locations
  • Type TW - dry or wet
  • THHN - dry, high temps
  • THW and THWN - wet, high temps
  • XHHW - high moisture heat resistance
  • UF - direct burial in soil but not concrete

16
Wire Identification
  • Color coded black, red, blue positive or hot
    wires which carry current to appliances
  • White neutral wires carry current from
    appliance back to source
  • Green or Bare ground all metal boxes and
    appliances

17
Wire Identification
  • Wire Size 12-2 has two strands of No. 12 wire
    (black white)
  • 12-2 w/g same, with one green or bare
  • 12-3 has three strands of No. 12 (black, red,
    white)
  • 12-3 w/g same, with green or bare

18
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